Imaging devices such as CCD and CMOS imaging devices for use in digital cameras and the like perform a photoelectric conversion of light received through a color filter to output image data. The color filter includes an RGB color filter, a YMCK color filter and the like. A single-chip imaging device having a color filter outputs image data about one color per pixel. For example, an imaging device having the RGB color filter outputs image data about an R (red) component, a C (green) component or a B (blue) component per pixel.
Thus, image data outputted from a single-chip imaging device including the color filter is processed in such a manner that because only the image data about one color per pixel is outputted, the image data about the remaining color components is subjected to an interpolation process. Various algorithms are used for this interpolation process.
Because the interpolation process is the process of inferring image data about a target pixel from image data about its surrounding pixels, there are cases in which incorrect interpolation occurs depending on the contents of images. To solve the problem, a method has been carried out which calculates a difference signal between vertical signals of the same color and a difference signal between horizontal signals of the same color to determine the degree of correlation in the vertical direction and the horizontal direction, thereby interpolating pixels in accordance with this degree of correlation.
Patent Documents 1 and 2 to be described below disclose inventions intended for obtaining an image with reduced image blurring and reduced level variations by repeating the interpolation process of color difference signals twice.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-128564
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-140495